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Abstract:

There are many inventions described and illustrated herein. In one aspect,
the present invention is directed to a technique of fabricating or
manufacturing MEMS having mechanical structures that operate in
controlled or predetermined mechanical damping environments. In this
regard, the present invention encapsulates the mechanical structures
within a chamber, prior to final packaging and/or completion of the MEMS.
The environment within the chamber containing and/or housing the
mechanical structures provides the predetermined, desired and/or selected
mechanical damping. The parameters of the encapsulated fluid (for
example, the gas pressure) in which the mechanical structures are to
operate are controlled, selected and/or designed to provide a desired
and/or predetermined operating environment.

Claims:

1. An electromechanical device comprising:a chamber including a first
encapsulation layer having at least one vent;a mechanical structure,
wherein the mechanical structure is disposed in the chamber; anda second
encapsulation layer, deposited over or in the vent, to thereby seal the
chamber, wherein the chamber includes at least one relatively stable gas.

2. The electromechanical device of claim 1, wherein the second
encapsulation layer is deposited using an epitaxial, a sputtering or a
CVD reactor.

3. The electromechanical device of claim 2, wherein the first
encapsulation layer is deposited using an epitaxial, a sputtering or a
CVD reactor.

7. The electromechanical device of claim 5, wherein the second
encapsulation layer is a metal bearing material.

8. The electromechanical device of claim 7, wherein the metal bearing
material is a silicide.

9. The electromechanical device of claim 1, wherein the relatively stable
gas has a low diffusivity.

10. The electromechanical device of claim 1, further including a third
encapsulation layer, disposed over the second encapsulation layer, to
reduce the diffusion of the fluid from the chamber.

11. The electromechanical device of claim 10, wherein the third
encapsulation layer is a metal bearing material.

12. The electromechanical device of claim 11, wherein the metal bearing
material is deposited using an epitaxial, a sputtering or a CVD reactor.

13. The electromechanical device of claim 10, wherein the third
encapsulation layer is at least one of monocrystalline silicon,
polycrystalline silicon, silicon dioxide, BPSG, PSG, silicon nitride or
silicon carbide.

14. The electromechanical device of claim 1, further including a third
encapsulation layer, disposed over the second encapsulation layer, to
reduce the diffusion of the fluid from the chamber, wherein the fluid
includes helium, neon or hydrogen that was diffused through the second
encapsulation layer and into the chamber to adjust the pressure of the
fluid to be within a predetermined range of pressures.

15. The electromechanical device of claim 14, wherein the third
encapsulation layer is a metal bearing material.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001]This application is a divisional of, and incorporates herein by
reference in its entirety the contents of, U.S. patent application Ser.
No. 10/392,528, which was filed on Mar. 20, 2003.

BACKGROUND

[0002]This invention relates to electromechanical systems and techniques
for fabricating microelectromechanical and nanoelectromechanical systems;
and more particularly, in one aspect, to fabricating or manufacturing
microelectromechanical and nanoelectromechanical systems having
microstructures encapsulated in a relatively stable, controlled pressure
environment to provide, for example, a predetermined, desired and/or
selected mechanical damping of the microstructure.

[0003]Microelectromechanical systems ("MEMS"), for example, gyroscopes,
resonators and accelerometers, utilize micromachining techniques (i.e.,
lithographic and other precision fabrication techniques) to reduce
mechanical components to a scale that is generally comparable to
microelectronics. MEMS typically include a mechanical structure
fabricated from or on, for example, a silicon substrate using
micromachining techniques.

[0004]In order to protect the delicate mechanical structure, MEMS are
typically packaged in, for example, a hermetically sealed metal container
(for example, a TO-8 "can," see, for example, U.S. Pat. No. 6,307,815) or
bonded to a semiconductor or glass-like substrate having a chamber to
house, accommodate or cover the mechanical structure (see, for example,
U.S. Pat. Nos. 6,146,917; 6,352,935; 6,477,901; and 6,507,082). In this
regard, in the context of the hermetically sealed metal container, the
substrate on, or in which, the mechanical structure resides may be
disposed in and affixed to the metal container. In contrast, in the
context of the semiconductor or glass-like substrate packaging technique,
the substrate of the mechanical structure may be bonded to another
substrate whereby the bonded substrates form a chamber within which the
mechanical structure resides. In this way, the operating environment of
the mechanical structure may be controlled and the structure itself
protected from, for example, inadvertent contact.

[0005]When employing such conventional packaging techniques, the resulting
MEMS tend to be quite large due primarily to packaging requirements or
constraints. In this regard, conventional MEMS packaging techniques often
produce finished devices that are quite large relative to the small
mechanical structure. In the context of packaging in a metal container,
this is due to the size of the container itself since it is quite large
relative to the mechanical structure. Where the MEMS employs a substrate
packaging technique, the substrate on or in which the mechanical
structure resides must have a sufficient periphery to permit or
facilitate the two substrates to be bonded using, for example, epoxy,
fusion, glass frit or anodic techniques. That periphery tends to
significantly increase the size of the resulting MEMS.

[0006]The operation of the MEMS depends, to some extent, on the
environment in which the mechanical structure is contained and is to
operate (for example, the pressure within the metal container). MEMS such
as accelerometers tend to operate more effectively in high damping
environments whereas gyroscopes and resonators tend to operate more
effectively in low damping environments. Accordingly, the mechanical
structures that comprise the accelerometer are often packaged in a high
pressure environment. In contrast, the mechanical structures that
comprise gyroscopes and resonators are often packaged and maintained in a
low pressure environment. For example, when gyroscopes and resonators are
packaged in a metal container, the pressure in the container is reduced,
and often the ambient gases are substantially evacuated, prior to
sealing.

[0007]There is a need for MEMS (for example, gyroscopes, resonators,
temperature sensors and/or accelerometers) that (1) overcome one, some or
all of the shortcomings of the conventional packaging techniques and (2)
include a controlled or controllable environment for proper, enhanced
and/or optimum operation of the mechanical structures.

SUMMARY OF THE INVENTION

[0008]There are many inventions described and illustrated herein. In a
first principal aspect, the present invention is a method of sealing a
chamber of an electromechanical device (for example, a
microelectromechanical or a nanoelectromechanical device) having a
mechanical structure, wherein the mechanical structure is in the chamber
and the chamber includes a fluid that is capable of providing mechanical
damping for the mechanical structure. The method of this aspect of the
invention includes depositing a first encapsulation layer over a
sacrificial layer that is disposed over at least a portion of the
mechanical structure. At least one vent is formed through the
encapsulation layer to expose at least a portion of the sacrificial layer
and at least a portion of the sacrificial layer is removed to form the
chamber. The method further includes introducing at least one relatively
stable gas into the chamber while depositing a second encapsulation layer
over or in the vent whereby when the chamber is sealed, the fluid within
the chamber includes the relatively stable gas(es).

[0010]In another embodiment of this aspect of the invention, the second
encapsulation layer may include a silicon-bearing compound, for example,
monocrystalline silicon, polycrystalline silicon, silicon dioxide,
silicon carbide, silicides, BPSG, PSG or silicon nitride. The second
encapsulation layer may be deposited using an epitaxial or a CVD reactor.

[0011]In another principal aspect, the present invention is a method of
sealing a chamber of an electromechanical device (for example, a
microelectromechanical or a nanoelectromechanical device) having a
mechanical structure, wherein the mechanical structure is in the chamber
and wherein the chamber includes a fluid that is capable of providing
mechanical damping for the mechanical structure. The method of this
aspect of the invention includes depositing a first encapsulation layer
over the mechanical structure, forming at least one vent through the
encapsulation layer and forming the chamber. The method further includes
depositing a second encapsulation layer by introducing at least one
gaseous deposition reagent into an epitaxial or CVD reactor to thereby
form a second encapsulation layer over or in the vent to thereby seal the
chamber. The fluid within the chamber includes at least one by-product
resulting from depositing a second encapsulation layer and wherein the
pressure of the fluid is sufficient to provide a predetermined mechanical
damping for the mechanical structure.

[0012]In one embodiment, the method further includes introducing at least
one relatively stable gas into the chamber while depositing the second
encapsulation layer over or in the vent. The fluid in the chamber may
also include the relatively stable gas(es), in addition to the by-product
resulting from depositing a second encapsulation layer. In one
embodiment, the relatively stable gas(es) may be helium, nitrogen, neon,
argon, krypton, xenon and/or perfluorinated hydrofluorocarbons.

[0013]The second encapsulation layer of this aspect of the present
invention may include a silicon-bearing compound, for example, a
polycrystalline silicon, silicon dioxide, silicon carbide, silicides,
BPSG, PSG or silicon nitride. The second encapsulation layer may be
deposited using an epitaxial or a CVD reactor. Indeed, the method may
also include heating the fluid in the chamber to adjust the pressure of
the fluid to be within a predetermined range of pressures.

[0014]In yet another principal aspect, the present invention is an
electromechanical device, for example, a microelectromechanical or
nanoelectromechanical device, including a chamber having a first
encapsulation layer disposed thereon. The first encapsulation layer
includes at least one vent. The electromechanical device also includes a
mechanical structure, which is disposed in the chamber. A second
encapsulation layer, deposited over or in the vent, seals the chamber
wherein the chamber includes at least one relatively stable gas (for
example, helium, nitrogen, neon, argon, krypton, xenon or perfluorinated
hydrofluorocarbons (such as, CF4 and C2F6), and/or
combinations thereof).

[0015]In one embodiment, the second encapsulation layer is deposited using
an epitaxial, a sputtering or a CVD reactor. In another embodiment, the
first encapsulation layer is also deposited using an epitaxial, a
sputtering or a CVD reactor.

[0017]The electromechanical device of this aspect of the present invention
may include a third encapsulation layer, disposed over the second
encapsulation layer, to reduce the diffusion of the fluid. In one
embodiment, the third encapsulation layer is a metal (for example,
aluminum, chromium, gold, silver, molybdenum, platinum, palladium,
tungsten, titanium, and/or copper), metal oxide (for example, aluminum
oxide, tantalum oxide, and/or indium oxide), metal alloy (for example,
titanium-nitride, titanium-tungsten and/or Al--Si--Cu) and/or
metal-silicon compound (for example, silicides such as tungsten silicide,
titanium silicide, and/or nickel silicide) (hereinafter, collectively
called "metal bearing material(s)") which is deposited using an
epitaxial, a sputtering or a CVD reactor. In another embodiment, the
third encapsulation layer is at least one of monocrystalline silicon,
polycrystalline silicon, silicon dioxide, BPSG, PSG, silicon nitride or
silicon carbide.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]In the course of the detailed description to follow, reference will
be made to the attached drawings. These drawings show different aspects
of the present invention and, where appropriate, reference numerals
illustrating like structures, components, materials and/or elements in
different figures are labeled similarly. It is understood that various
combinations of the structures, components, materials and/or elements,
other than those specifically shown, are contemplated and are within the
scope of the present invention.

[0019]FIG. 1 is a block diagram of microelectromechanical system disposed
on a substrate, in conjunction with interface circuitry and data
processing electronics;

[0020]FIG. 2 illustrates a top view of a portion of micromechanical
structure, for example, or portion of the interdigitated or comb-like
finger electrode arrays of an accelerometer;

[0021]FIG. 3 illustrates a cross-sectional view of the portion of the
interdigitated or comb-like finger electrode array of FIG. 2, sectioned
along dotted line a-a, in accordance with certain aspect of the present
invention;

[0022]FIGS. 4A-4F illustrate cross-sectional views of the fabrication of
the microstructure of FIG. 3 at various stages of an encapsulation
process, according to certain aspects of the present invention;

[0023]FIG. 5 illustrates a cross-sectional view of the portion of the
interdigitated or comb-like finger electrode array of FIG. 2, sectioned
along dotted line a-a, in accordance with another aspect of the present
invention where the first and second encapsulation layers are comprised
of the same material;

[0024]FIG. 6 illustrates a cross-sectional view of the portion of the
interdigitated or comb-like finger electrode array of FIG. 2, sectioned
along dotted line a-a, in accordance with another aspect of the present
invention where encapsulation layers are annealed such that the
encapsulation layers have the properties of a layer that was deposited in
one or substantially one processing step;

[0025]FIGS. 7A, 7B, and 8A-8C illustrate cross-sectional views of a
portion of the fabrication of the interdigitated or comb-like finger
electrode array microstructure of FIG. 2, sectioned along dotted line
a-a, in accordance with another aspect of the present invention where
encapsulation layers include three or more layers;

[0026]FIG. 9 illustrates a cross-sectional view of a portion of a
plurality of micromechanical structures, each having one or more
electromechanical systems, which are monolithically integrated on or
within the substrate of a MEMS, in accordance with certain aspect of the
present invention.

DETAILED DESCRIPTION

[0027]There are many inventions described and illustrated herein. In one
aspect, the present invention is directed to a technique of fabricating
or manufacturing MEMS having mechanical structures that operate in
controlled or predetermined mechanical damping environments. In this
regard, the present invention encapsulates the mechanical structures
within a chamber, prior to final packaging and/or completion of the MEMS.
The environment within the chamber containing and/or housing the
mechanical structures provides the predetermined, desired and/or selected
mechanical damping. The parameters (for example, pressure) of the
encapsulated fluid (for example, a gas or a gas vapor) in which the
mechanical structures are to operate are controlled, selected and/or
designed to provide a desired and/or predetermined operating environment.

[0028]In one embodiment, one or more relatively stable gases, having a
selected, desired and/or predetermined state(s), are introduced during
the encapsulation process. The relatively stable gas(es) experiences
little to no reaction, during the encapsulation process, with, for
example, the mechanical structures, materials used to encapsulate the
mechanical structures (i.e., the deposition reagents) and/or the products
produced during the process (whether in a gas or solid form). As such,
once the chamber containing and/or housing the mechanical structures is
"sealed" by way of the encapsulation process, the relatively stable gas
is "trapped" within the chamber. The state of the gas(es) within the
chamber determine, to a significant extent, the predetermined, desired
and/or selected mechanical damping of the mechanical structures.

[0029]This relatively stable gas(es), for example, helium, nitrogen, neon,
argon, krypton, xenon and/or perfluorinated hydrofluorocarbons (for
example, CF4 and C2F6), may comprise the majority, all or
substantially all of the fluid within the sealed chamber (i.e., the
chamber containing the encapsulated mechanical structures). In a
preferred embodiment, the relatively stable gas(es) includes a low,
well-known and/or controllable diffusivity during and after encapsulation
process. In this way, the state of the gas(es) may be controlled,
selected and/or designed to provide a desired and/or predetermined
environment over the operating lifetime of the finished MEMS and/or
after, for example, subsequent micromachining processing (for example,
high temperature processes).

[0030]In another embodiment, one or more gases are introduced during the
encapsulation process with the expectation that those gases will react
with the environment during and/or after the encapsulation process. In
this embodiment, the predetermined gases react and/or combine with
gas(es), material(s) and/or by-product(s) resulting from, or produced
during the encapsulation process, to provide a desired and/or
predetermined fluid (having a desired, selected and/or predetermined
state) that is trapped within the "sealed" chamber containing the
encapsulated mechanical structures. In this way, the fluid, having a
selected, desired and/or predetermined state, resides or is maintained
within the chamber containing the mechanical structures and provides a
desired, predetermined and/or selected mechanical damping for those
structures.

[0031]The one or more gases may be a primary or a secondary reagent in the
forming, growing and/or depositing the encapsulation layer(s).
Alternatively, (or in addition to) these gases may be additional gases
that are not significant in forming, growing and/or depositing the
encapsulation layer(s). In this regard, these additional gases may react
with materials (solids and/or gases) in the deposition environment to
produce by-product(s) that are trapped in the chamber after
encapsulation.

[0032]It should be noted that the state of the fluid that is trapped may
be adjusted, modified and/or controlled by subsequent processing steps.
In this regard, the state of the fluid (for example, the pressure)
immediately after encapsulation may be adjusted, modified and/or
controlled by a subsequent micromachining and/or integrated circuit
processing which may cause or promote, for example, (1) additional
reaction(s) between the "trapped" fluid and the other elements of the
environment within the chamber (for example, the material surrounding or
comprising the mechanical structures) and/or (2) diffusion of the
"trapped" fluid or by-products thereof. As such, in certain embodiments,
the fluid that is trapped within the sealed chamber may undergo further
change during and/or after encapsulation process such that, after
completion of the MEMS, the state of the fluid within the sealed chamber
provides the desired, predetermined and/or selected mechanical damping
for the mechanical structures. Thus, in these embodiments, the state of
the fluid may be adjusted, modified and/or controlled to provide the
desired and/or predetermined environment over the operating lifetime of
the finished MEMS and/or after subsequent micromachining and/or
integrated circuit processing.

[0033]With reference to FIG. 1, in one exemplary embodiment, a MEMS 10
includes a micromachined mechanical structure 12 that is disposed on
substrate 14, for example, an undoped semiconductor-like material, a
glass-like material, or an insulator-like material. The MEMS 10 may also
include data processing electronics 16, to process and analyze
information generated by micromachined mechanical structure 12. In
addition, MEMS 10 may also include interface circuitry 18 to provide the
information from micromachined mechanical structure 12 and/or data
processing electronics 16 to an external device (not illustrated), for
example, a computer, indicator or sensor.

[0034]The data processing electronics 16 and/or interface circuitry 18 may
be integrated in or on substrate 14. In this regard, MEMS 10 may be a
monolithic structure including mechanical structure 12, data processing
electronics 16 and interface circuitry 18. The data processing
electronics 16 and/or interface circuitry 18 may also reside on a
separate, discrete substrate that, after fabrication, is bonded to or on
substrate 14.

[0035]With reference to FIG. 2, in one embodiment, micromachined
mechanical structure 12 includes mechanical structures 20a-d disposed on,
above or in substrate 14. The micromachined mechanical structure 12 may
be an accelerometer, gyroscope or other transducer (for example, pressure
sensor, tactile sensor or temperature sensor). The micromachined
mechanical structure 12 may also include mechanical structures of a
plurality of transducers or sensors including one or more accelerometers,
gyroscopes, pressure sensors, tactile sensors and temperature sensors.
Where micromachined mechanical structure 12 is an accelerometer,
mechanical structures 20a-d may be a portion of the interdigitated or
comb-like finger electrode arrays that comprise the sensing features of
the accelerometer (See, for example, U.S. Pat. No. 6,122,964).

[0037]It should be noted that the mechanical structures of one or more
transducers or sensors (for example, accelerometers, gyroscopes, pressure
sensors, tactile sensors and/or temperature sensors) may be contained or
reside in a single chamber. Under this circumstance, fluid 24 in chamber
22 provides a desired, predetermined, appropriate and/or selected
mechanical damping for the mechanical structures of one or more
micromachined mechanical structures (for example, an accelerometer, a
pressure sensor, a tactile sensor and/or temperature sensor).

[0038]Moreover, the mechanical structures of the one or more transducers
or sensors may themselves include multiple layers that are vertically
stacked and/or interconnected. (See, for example, micromachined
mechanical structure 12b of FIG. 9). Thus, under this circumstance, the
mechanical structures are fabricated using one or more processing steps
to provide the vertically stacked and/or interconnected multiple layers.

[0039]In one embodiment, fluid 24 is primarily one or more relatively
stable gases (for example, helium, nitrogen, neon, argon, krypton, xenon
and/or perfluorinated hydrofluorocarbons such as, CF4 and
C2F6). In another embodiment, fluid 24 is one or more gases or
gas/fluid product(s) (for example,
SiH4+O2→SiO2+H2O+O2) that are used in,
result from or are produced by or during, the encapsulation process
and/or a subsequent fabrication process or processes. Indeed, fluid 24
may be a combination of one or more relatively stable gases and one or
more other gases or product(s) that result from, or are produced by, the
encapsulation process.

[0040]The encapsulating layers 26a and 26b may be comprised of, for
example, a semiconductor, an insulator or a metal bearing material. For
example, the encapsulating layers 26a and 26b may contain silicon (for
example, monocrystalline silicon, polycrystalline silicon or amorphous
silicon, whether doped or undoped), and/or nitrogen (for example, a
silicon nitride) and/or oxygen (for example, a silicon dioxide). Other
materials are suitable for encapsulating or sealing chamber 22 (for
example, germanium, silicon/germanium, silicon carbide (SiC), and gallium
arsenide). Indeed, all materials that are capable of encapsulating
chamber 22 and providing an adequate barrier to diffusion of fluid 24,
whether now known or later developed, are intended to be within the scope
of the present invention.

[0041]The encapsulating layers 26a and 26b may be the same materials or
different materials. The encapsulating layers 26a and 26b may be
deposited, formed or grown using the same or different techniques. For
example, encapsulating layer 26a may be a polycrystalline silicon
deposited using a low pressure ("LP") chemically vapor deposited ("CVD")
process or plasma enhanced ("PE") CVD process and encapsulating layer 26b
may be a polycrystalline silicon deposited using an atmospheric pressure
("AP") CVD process. Alternatively, for example, encapsulating layer 26a
may be a silicon dioxide deposited using a LPCVD process and
encapsulating layer 26b may be a doped silicon dioxide (for example,
phosphosilicate ("PSG") or borophosphosilicate ("BPSG")) using a PECVD
process. Indeed, encapsulating layer 26a may be a polycrystalline silicon
or doped silicon dioxide (for example, PSG or BPSG) using a PECVD process
and encapsulating layer 26b may be a silicon dioxide deposited using a
LPCVD. Thus, all materials and deposition techniques, and permutations
thereof, for encapsulating chamber 22, whether now known or later
developed, are intended to be within the scope of the present invention.

[0042]It should be noted that the encapsulating layers 26a and/or 26b may
be selected in conjunction with the selection of the one or more
predetermined gases in order to provide the gas/fluid product(s) that
result from or are produced by the encapsulation process and/or
subsequent fabrication process(es). For example, employing
SiH4+O2 may produce encapsulating layer 26b of SiO2 and
fluid 24 of H2O+O2. In another embodiment, employing SiO4
(CH4)x+O2 may produce encapsulating layer 26b of SiO2 and
fluid 24 of O2+various carbon containing by-products.

[0043]With reference to FIG. 4A, the exemplary method of fabricating or
manufacturing a micromachined mechanical structure 12 may begin with a
partially formed device including mechanical structures 20a-d disposed on
sacrificial layer 28, for example, silicon dioxide. Mechanical structures
20a-d and sacrificial layer 28 may be formed using well known deposition,
lithographic, etching and/or doping techniques.

[0044]With reference to FIGS. 4B, 4C and 4D, following formation of
mechanical structures 20a-d, second sacrificial layer 30, for example,
silicon dioxide or silicon nitride, may be deposited to secure, space
and/or protect mechanical structures 20a-d during subsequent processing.
Thereafter, first encapsulation layer 26a may be deposited on second
sacrificial layer 30 (see, FIG. 4C) and etched (see, FIG. 4D) to form
passages or vents 32 to permit etching and/or removal of selected
portions of first and second sacrificial layers 28 and 30, respectively.

[0045]With reference to FIGS. 4D and 4E, first and second sacrificial
layers 28 and 30, respectively, may be etched to remove selected portions
of layers 28 and 30 and release mechanical structures 20a-d. For example,
in one embodiment, where first and second sacrificial layers 28 and 30
are comprised of silicon dioxide, selected portions of layers 28 and 30
may be removed/etched using well known wet etching techniques and
buffered HF mixtures (i.e., a buffered oxide etch) or well known vapor
etching techniques using vapor HF. Proper design of mechanical structures
20a-d and sacrificial layers 28 and 30, and control of the HF etching
process parameters may permit the sacrificial layer 28 to be sufficiently
etched to remove all or substantially all of layer 28 around mechanical
elements 20a-d and thereby release mechanical elements 20a-d to permit
proper operation of MEMS 10.

[0046]In another embodiment, where first and second sacrificial layers 28
and 30 are comprised of silicon nitride, selected portions of layers 28
and 30 may be removed/etched using phosphoric acid. Again, proper design
of mechanical structures 20a-d and sacrificial layers 28 and 30, and
control of the wet etching process parameters may permit the sacrificial
layer 28 to be sufficiently etched to remove all or substantially all of
sacrificial layer 28 around mechanical elements 20a-d which will release
mechanical elements 20a-d.

[0047]It should be noted that there are: (1) many suitable materials for
layers 28 and/or 30 (for example, silicon dioxide, silicon nitride, and
doped and undoped glass-like materials, e.g., PSG, BPSG, and spin on
glass ("SOG")), (2) many suitable/associated etchants (for example, a
buffered oxide etch, phosphoric acid, and alkali hydroxides such as, for
example, NaOH and KOH), and (3) many suitable etching or removal
techniques (for example, wet, plasma, vapor or dry etching), to
eliminate, remove and/or etch sacrificial layers 28 and/or 30. Indeed,
layers 28 and/or 30 may be a doped or undoped semiconductor (for example,
polysilicon, germanium or silicon/germanium) in those instances where
mechanical structures 20a-d are the same or similar semiconductors (i.e.,
processed, etched or removed similarly) provided that mechanical
structures 20a-d are not affected by the etching or removal processes
(for example, where structures 20a-d are "protected" during the etch or
removal process (e.g., an oxide layer protecting a silicon based
structures 20a-d) or where structures 20a-d are comprised of a material
that is neither affected nor significantly affected by the etching or
removal process of layers 28 and/or 30). Accordingly, all materials,
etchants and etch techniques, and permutations thereof, for eliminating,
removing and/or etching, whether now known or later developed, are
intended to be within the scope of the present invention.

[0048]With reference to FIG. 4F, after releasing mechanical elements
20a-d, second encapsulation layer 26b may be deposited, formed and/or
grown. The second encapsulation layer 26b may be, for example, a
silicon-based material (for example, a polysilicon or silicon dioxide),
which is deposited using, for example, an epitaxial, a sputtering or a
CVD-based reactor (for example, APCVD, LPCVD, or PECVD). The deposition,
formation and/or growth may be by a conformal process or non-conformal
process. The material may be the same as or different from first
encapsulation layer 26a. However, it may be advantageous to employ the
same material to form first and second encapsulation layers 26a and 26b
(see, FIG. 5). In this way, the thermal expansion rates are the same and
the boundaries between layers 26a and 26b may enhance the "seal" of
chamber 24.

[0049]In one set of embodiments, during the deposition of second
encapsulation layer 26b, in addition to the gases that are employed to
form, deposit and/or grow layer 26b (for example,
SiH4→Si+2H2), one or more relatively stable gases (for
example, helium, nitrogen, neon, argon, xenon, and/or perfluorinated
hydrofluorocarbons) are introduced at a predetermined pressure and flow
rate. These relatively stable gases are trapped or encapsulated in
chamber 22, during the encapsulation process, to form part or all of
fluid 24. As mentioned above, fluid 24 provides an environment for
mechanical structures 20a-d with a desired, predetermined and/or selected
mechanical damping.

[0050]In certain embodiments, the one or more relatively stable gases have
or cause little to no reaction during the encapsulation process. For
example, the relatively stable gas does not significantly react with
mechanical structures 20a-d (for example, the sidewalls of structures
20a-d), the gases/materials used to encapsulate/seal the mechanical
structures 20a-d (for example, silicon, oxygen or nitrogen), first
encapsulation layer 26a, and/or second encapsulation layer 26b which is
formed, deposited and/or grown during the encapsulating/sealing process.
Thus, in these embodiments, once chamber 22 containing and/or housing the
mechanical structures 20a-d is "sealed" (i.e., after deposition of second
encapsulation layer 26b), the relatively stable gas is "trapped" within
chamber 22 and provides (or will provide after, for example, subsequent
processing steps that finalize the environment) mechanical structures
20a-d with a selected, designed and/or predetermined mechanical damping
parameter.

[0051]The relatively stable gas(es) may be, for example, any gas (or gas
compound) that is relatively stable or controllable: (1) during
formation, deposition and/or growth of second encapsulation layer 26b
(for example, at the pressure and temperature of the process and with the
reagents of that process) and/or (2) with respect to the environment
within chamber 22 (for example, causes little to no reaction with first
encapsulation layer 26a (for example, silicon dioxide or other
silicon-based material). In this way, the one or more relatively stable
gases will not react, or will only minimally react, with the deposition
reagents, the products, the encapsulated mechanical structure 12 and/or
the encapsulation walls during (and, preferably after) formation,
deposition and/or growth of second encapsulation layer 26b.

[0052]In a preferred embodiment, the one or more relatively stable gases
may be helium, nitrogen, neon, argon, krypton, xenon and/or
perfluorinated hydrofluorocarbons (for example, CF4 and
C2F6). The relatively stable gas(es) may comprise some, a
majority, all or substantially all of fluid 24 within chamber 22 after
sealing or isolating chamber 22.

[0053]As discussed in detail below, the state of the gas(es) during the
encapsulation process may determine the parameters of the gas(es) (and
the mechanical damping parameter of the MEMS 10) when sealed within
chamber 22. In this regard, the temperature of the encapsulation process
and the partial pressure of the relatively stable gas(es) may have a
significant impact on the pressure of fluid 24 after encapsulation. As
such, in those situations where a relatively high mechanical damping is
desired (for example, where micromachined mechanical structure 12 is an
accelerometer that requires a low quality factor (Q), it may be
advantageous to employ fabrication techniques for forming, depositing
and/or growing second encapsulation layer 26b having low temperatures and
high pressures. In this way, the final pressure of fluid 24 in chamber 22
may be relatively high.

[0054]For example, in one embodiment, where second encapsulation layer 26b
is a silicon dioxide (or other insulator, for example, silicon nitride)
using LPCVD techniques facilitates "sealing" chamber 22 at a relatively
low temperature. In this regard, LPCVD may generally be operated between
100 to 500 Pa and at a relatively low temperature, typically 500°
C. to 600° C. In another embodiment, an APCVD may be employed to
deposit doped and undoped oxides (for example, BPSG, PSG, and/or
SiO2) at relatively high pressures (100 to 10 k Pa) and low
temperatures (350° C. to 400° C.). In those instances where
second encapsulation layer 26b is a silicon-based material (polysilicon,
silicon carbide, silicon dioxide, and/or silicon nitride), an epitaxy
reactor may be employed to deposit such a material at pressures between 1
to 2 atmospheres and temperatures between 400° C. to 1200°
C.

[0055]It should be noted that there are many deposition techniques and
materials that are suitable for forming, depositing and/or growing second
encapsulation layer 26b. For example, a PECVD technique may be employed
to deposit, for example, doped and undoped oxides, silicon nitride
silicon carbide, and/or polysilicon at suitable pressures and
temperatures. All materials and formation, deposition and growth
techniques, and permutations thereof, for forming, depositing and/or
growing second encapsulation layer 26b, whether now known or later
developed, are intended to be within the scope of the present invention.

[0056]In those situations where micromachined mechanical structure 12
undergoes or experiences additional micromachining processing, it may be
advantageous to employ one or more relatively stable gases that include a
low, well-known and/or controllable diffusivity. For example, gases
having larger or heavier molecules (for example, nitrogen, neon, argon,
krypton, xenon or perfluorinated hydrofluorocarbons (for example,
CF4 and C2F6)) may be less susceptible to diffusion, via
first encapsulation layer 26a and/or second encapsulation layer 26b
(and/or at the boundaries thereof), during and after the encapsulation
process. In this way, the state of fluid 24 may be controlled, selected
and/or designed to provide the desired and/or predetermined environment
after, for example, subsequent micromachining processing (for example,
high temperature processes) and/or over the operating lifetime of the
finished MEMS 10. This may provide MEMS 10 that has or exhibits a more
stable and precise operation.

[0057]It should be noted that where micromachined mechanical structure 12
undergoes or is subjected to micromachining processing that may impact
the environment within chamber 22, fluid 24 may diffuse through
encapsulation layer 26a and/or encapsulation layer 26b. That diffusion
may cause or result in a "final" ambient pressure of fluid 24 (i.e., the
pressure of fluid 24 after completion of MEMS 10) being below or outside
of the selected, predetermined and/or desired range of pressures. As
such, in one embodiment, the ambient pressure of fluid 24 immediately
after being "trapped" or "sealed" in chamber 24 may be selected or
designed to be greater than the selected, predetermined and/or desired
range of mechanical damping of micromachined mechanical structure 12
required or desired during normal operation. Thus, after any diffusion of
fluid 24, as a result of additional processing, the "final" ambient
pressure of fluid 24 may be within the selected, predetermined and/or
desired range of pressures. In this way, the subsequent micromachining
processing causes a reduction in pressure of fluid 24 such that the
"final" pressure of fluid 24 provides the selected, designed or
predetermined mechanical damping of micromachined mechanical structure
12.

[0058]It should be further noted that in those situations where second
encapsulation layer 26b (and first encapsulation layer 26a) are comprised
of a dense material, it may be advantageous to employ relatively stable
gas(es) such as hydrogen and/or helium in addition to, or in lieu of, for
example, nitrogen, neon, argon, krypton, xenon and/or perfluorinated
hydrofluorocarbons (for example, CF4 and C2F6). A second
encapsulation layer 26b (and first encapsulation layer 26a) that is
comprised of a dense material, for example, silicon carbide, silicon
nitride, or metal bearing material, may provide a sufficient barrier to
diffusion which thereby permits use of relatively stable gases that are
light, have small molecules and are relatively inexpensive and available,
such as hydrogen and/or helium.

[0059]In another set of embodiments, during the deposition, growth and/or
formation of second encapsulation layer 26b, one or more gases/materials
are introduced to form, deposit and/or grow second encapsulation layer
26b (for example, SiH4→Si+2H2), with the expectation
that these gases will react during the encapsulation process to provide a
resulting fluid (having a desired, selected and/or predetermined state)
that is trapped within chamber 22--after second encapsulation layer 26b
"seals" chamber 22. In these embodiments, the predetermined gas/material
are primary or secondary reagents of the deposition process and, in
addition to being major/secondary constituents in the formation of second
encapsulation layer 26b, also provide fluid 24 (having a desired,
selected and/or predetermined state) that is "trapped" within chamber 22.
In this way, fluid 24 provides a desired, predetermined and/or selected
mechanical damping for the structures 20a-d.

[0060]Thus, in these embodiments, the predetermined gas/material are
primary or secondary reagents of the deposition process to react and/or
combine with a gas, material(s) and/or by-product(s) produced during the
encapsulation process.

[0061]For example, in one embodiment, where the second encapsulation layer
26b is silicon dioxide (for example,
SiH4+O2→SiO2+H2O+O2), an APCVD may be
employed to deposit the oxide at relatively high pressures (100 to 10
kPa) and low temperatures (350° C. to 400° C.). The
residual H2O+O2 (i.e., fluid 24) may be "trapped" in chamber 22
at a relatively high pressure and relatively low temperature. Indeed,
where necessary or desired, the pressure of fluid 24 may be adjusted or
modified during subsequent processing steps to provide the desired,
predetermined and/or selected mechanical damping for mechanical
structures 20a-d.

[0062]In another embodiment, an epitaxy reactor may be employed to deposit
the second encapsulation layer 26b as a polysilicon at pressures between
1 to 2 atmospheres and temperatures between 400° C. to
1200° C. (for example, SiCl4 (gas)+2H2→Si
(solid)+4HCl (gas)). The fluid 24 (i.e., 4HCl) may be "trapped" in
chamber 22 at a desired, predetermined and/or selected pressure and
relatively low temperature. As such, fluid 24, having a selected, desired
and/or predetermined state, may provide a desired, predetermined and/or
selected mechanical damping for the structures 20a-d.

[0063]As mentioned above, there are many deposition techniques and
materials that are suitable for forming, depositing and/or growing second
encapsulation layer 26b. For example, a CVD technique may be employed to
deposit, for example, doped and undoped oxides (for example,
SiO4(CH4)x+O2→SiO2 (encapsulating layer
26b)+O2 (fluid 24)+a carbon by-product (fluid 24)), as well as
silicon nitride and/or polysilicon. Accordingly, all materials and
formation, deposition and growth techniques, and permutations thereof,
for forming, depositing and/or growing second encapsulation layer 26b,
whether now known or later developed, are intended to be within the scope
of the present invention.

[0064]It should be noted that the residual gas(es) may be trapped in
chamber 22 at a desired, predetermined and/or selected pressure.
Moreover, where the trapped gas(es) is not at a (or within a range of)
desired, predetermined and/or selected "final" pressure, the pressure of
the gas(es) may be modified, changed and/or controlled, via subsequent
process (for example, high temperature processing that causes diffusion
or further/continuing reactions), so that the "completed" MEMS 10
includes a micromachined mechanical structure 12 that is properly damped
(i.e., at, or within a range of, the desired, predetermined and/or
selected mechanical damping for structure 12). Thus, the state of fluid
24 (for example, the pressure of fluid 24) immediately after
encapsulation may be adjusted, modified and/or controlled by a subsequent
micromachining and/or integrated circuit processing. In this way, the
state of fluid 24 may be adjusted, modified and/or controlled to provide
a desired and/or predetermined environment over the operating lifetime of
the finished MEMS and/or after subsequent micromachining and/or
integrated circuit processing.

[0065]In another set of embodiments, the one or more additional
gases/materials react with the environment (for example, solids and/or
gases in and/or around micromachined mechanical structure 12, mechanical
structures 20a-d and/or chamber 22) to provide fluid 24 that is "trapped"
in chamber 22 after chamber 22 is "sealed". However, in these
embodiments, the one or more gases/materials do not have a significant
role in forming, growing and/or depositing encapsulation layer 26b. In
these embodiments, the predetermined gas/material are in addition to the
primary or secondary reagents of the deposition process and react with
the environment during encapsulation to provide fluid 24 (having a
desired, selected and/or predetermined state) that is "trapped" within
chamber 22. As mentioned above, fluid 24 provides a desired,
predetermined and/or selected mechanical damping for structures 20a-d.

[0066]For example, in one embodiment, where second encapsulation layer 26b
is silicon dioxide (for example, O2+2Si→SiO2+2SiO) an
APCVD may be employed to deposit the oxide at relatively high pressures
(100 to 10 kPa) and low temperatures (350° C. to 400° C.).
The residual 2SiO (i.e., fluid 24) may be "trapped" in chamber 22 at a
relatively high pressure and relatively low temperature. As mentioned
above, where necessary or desired, the pressure of fluid 24 may also be
adjusted or modified during subsequent processing steps to provide the
desired, predetermined and/or selected mechanical damping for mechanical
structures 20a-d. As mentioned above, in those situations where a
relatively high mechanical damping is desired (for example, where
micromachined mechanical structure 12 is an accelerometer that requires a
low Q), it may be advantageous for the final pressure of fluid 24 in
chamber 22 to be relatively high. As such, where a relatively high
pressure of fluid 24 is desired, it may be advantageous to employ low
temperature techniques for depositing, forming and/or growing second
encapsulation layer 26b. In this regard, as the sealing temperature is
decreased, the pressure at the operating temperature will increase by
approximately the ratio of the absolute temperatures. As such, lower
"sealing" temperatures may contribute to a higher pressure of fluid 24
when chamber 22 is "sealed".

[0067]Moreover, it may be important that the partial pressure of the
gas/material that comprises fluid 24 be relatively high so that the
pressure of fluid 24 that resides or is "trapped" in "sealed" chamber 22
is relatively high. In this regard, as the partial pressure of the gas
(for example, the relatively stable gas) increases during the
encapsulation or chamber sealing process (i.e., during the deposition,
formation and/or growth of second encapsulation layer 26b), the pressure
of fluid 24 in chamber 22 increases proportionally. As such, it may be
advantageous to minimize or reduce the flow of other process gases during
the encapsulation process in those situations where it is desired to have
a high final pressure of fluid 24.

[0068]It should also be noted that, in those situations where a high final
pressure of fluid 24 is desired, it may also be advantageous to implement
the encapsulation process (i.e., the process of depositing, forming
and/or growing second encapsulation layer 26b) at a high, elevated and/or
maximum total pressure to enhance and/or maximize the final pressure of
fluid 24. In this way, a relatively high mechanical damping of
micromachined mechanical structure 12 may be achieved.

[0069]It should be further noted that, in certain embodiments, the
encapsulation layer that "traps" and "seals" fluid 24 in chamber 22 may
be sufficiently annealed to function as if the encapsulation layers 26a
and 26b were deposited, formed and/or grown during one or substantially
one processing step (see, FIG. 6). Such an encapsulation layer may
provide a better "seal" of chamber 22 so that fluid 24 is less
susceptible to diffusion over the lifetime of the MEMS and/or under harsh
external operating environments. Moreover, the encapsulation process of
chamber 22 may include three or more encapsulation layers. With reference
to FIGS. 7A and 7B, in another set of embodiments, a second encapsulation
layer 26b may be deposited, formed and/or grown. In this set of
embodiments, however, second encapsulation layer 26b does not entirely
"seal" chamber 22. Rather, a third encapsulation layer 26c (or subsequent
layer 26x) "seals" chamber 22 and "traps" fluid 24 in chamber 22.

[0070]The second encapsulation layer 26b may be, for example, a
semiconductor material (for example, a monocrystalline, polycrystalline
silicon or germanium), an insulator material (for example, silicon
dioxide, silicon nitride, BPSG, or PSG) or metal bearing material (for
example, suicides or TiW), which is deposited using, for example, an
epitaxial, a sputtering or a CVD-based reactor (for example, APCVD, LPCVD
or PECVD). The deposition, formation and/or growth may be by a conformal
process or non-conformal process. The material comprising encapsulation
layer 26b may be the same as or different from first encapsulation layer
26a.

[0072]The deposition, formation and/or growth of third encapsulation layer
26c may be the same as, substantially similar to, or different from that
of encapsulation layers 26a and/or 26b. In this regard, third
encapsulation layer 26c may be comprised of, for example, a semiconductor
material, an insulator material, or metal bearing material. The third
encapsulation layer 26c may be deposited using, for example, an
epitaxial, a sputtering or a CVD-based reactor (for example, APCVD, LPCVD
or PECVD). The deposition, formation and/or growth process may be
conformal or non-conformal. The material comprising encapsulation layer
26c may be the same as or different from first encapsulation layer 26a
and/or second encapsulation layer 26b.

[0073]As mentioned above, it may be advantageous to employ the same
material to form first and second encapsulation layers 26a and 26b and/or
second and third encapsulation layers 26b and 26c. In this way, the
thermal expansion rates are the same and the boundaries between layers
26a and 26b may enhance the "seal" of chamber 24.

[0074]It should be noted that the entire discussion above with respect to
fluid 24 and/or fluid 24 in conjunction with FIGS. 3-6 is entirely, fully
and completely applicable to this set of embodiments. For the sake of
brevity, it will not be repeated.

[0075]With reference to FIGS. 8A and 8B, in another set of embodiments,
encapsulation layer 26c (FIG. 8A) and encapsulation layer 26d (FIG. 8B)
may be deposited, formed and/or grown to enhance the "seal" of chamber 22
and thereby enhance the barrier to diffusion of fluid 24. The
encapsulation layer 26c (FIG. 8A) and encapsulation layer 26d (FIG. 8B),
alone, or in combination with the other encapsulation layers, "traps"
fluid 24 (having a selected, desired and/or predetermined state) in
chamber 22.

[0076]The encapsulation layer 26c (FIG. 8A) and encapsulation layer 26d
(FIG. 8B) may be, for example, a semiconductor material (for example, a
polysilicon, germanium, or silicon/germanium), an insulator material (for
example, silicon dioxide, silicon nitride, BPSG, PSG, or SOG) or metal
bearing material (for example, silicides). The encapsulation layer 26c
(FIG. 8A) and encapsulation layer 26d (FIG. 8B) may be, for example
deposited, formed or grown using, for example, an epitaxial, a sputtering
or a CVD-based reactor (for example, APCVD, LPCVD or PECVD). The
deposition, formation and/or growth may be by a conformal process or
non-conformal process. The material comprising encapsulation layer 26c
(FIG. 8A) and encapsulation layer 26d (FIG. 8B) may be the same as or
different from the other encapsulation layers.

[0077]It should be noted that the discussion above with respect to fluid
24 and/or fluid 24 in conjunction with FIGS. 3-6 is entirely, fully and
completely applicable to this set of embodiments. For the sake of
brevity, it will not be repeated.

[0078]It should be further noted that encapsulation layer 26b (FIG. 8A)
and encapsulation layer 26c (FIG. 8B), in addition to or in lieu of
providing a barrier to diffusion of fluid 24, may be employed to reduce,
minimize and/or eliminate any step coverage issues that may be presented
when enclosing or "sealing" passages or vents 32 (see, for example, FIGS.
4E, 4F, 7A and 7B) and chamber 22. In this regard, encapsulation layer
26b (FIG. 8A) and encapsulation layer 26c (FIG. 8B) may be a material
that is deposited, formed and/or grown in a manner that provides good,
enhanced, adequate and/or sufficient step coverage, for example, BPSG,
PSG or SOG which is deposited using, for example, a CVD-based reactor
(for example, APCVD, LPCVD or PECVD). In this way, encapsulation layer
26b (FIG. 8A) and encapsulation layer 26c (FIG. 8B) may provide, or if
necessary may be further processed to provide (for example, a re-flow
step), a sufficiently and/or substantially planar surface.

[0080]In addition, with reference to FIG. 8C, an additional encapsulation
layer 26d may be deposited, formed and/or grown to further enhance the
"seal" of chamber 22. In this embodiment, encapsulation layer 26c may
provide some, little or no barrier to diffusion of fluid 24 whereas
encapsulation layer 26d presents some, a majority or essentially the
entire barrier to diffusion of fluid 24. Thus, encapsulation layer 26d,
alone or together with the other encapsulation layers (i.e.,
encapsulation layers 26a-c), "traps" fluid 24 in chamber 22.

[0081]Further, as noted above, encapsulation layers 26b and/or
encapsulation layer 26c may be employed (alone or in combination) to
reduce, minimize and/or eliminate any step coverage issues that may be
presented by enclosing passages or vents 32 and "sealing" chamber 22. The
encapsulation layer 26b and/or encapsulation layer 26c may provide a
sufficiently and/or substantially planar surface so that encapsulation
layer 26c and/or encapsulation layer 26d may be implemented using a wide
variety of material(s) and deposition, formation and/or growth techniques
in order to "seal" of chamber 22 and "trap" fluid 24 (having a selected,
desired and/or predetermined state) in chamber 22.

[0082]Accordingly, in this set of embodiments, at least one additional
encapsulation layer 26d is deposited, formed and/or grown over a fully
encapsulated and "sealed" chamber 22 to provide an additional barrier to
diffusion of fluid 24. In this way, fluid 24 is "trapped" in chamber 22
and has a selected, desired and/or predetermined state to facilitate
proper operation of mechanical structure 12.

[0083]With reference to FIGS. 8A-C, in another set of embodiments, some, a
majority, all or substantially all of fluid 24 is "trapped" within
chamber 22 (and the state of fluid 24 is established within a selected,
predetermined and/or desired range of pressures) after depositing,
forming or growing encapsulation layer 26b (FIG. 8A) and encapsulation
layer 26c (FIG. 8B) while depositing, forming or growing encapsulation
layer 26c (FIG. 8A) and encapsulation layer 26d (FIG. 8B). In this set of
embodiments, fluid 24 may be diffused into chamber 22 after enclosed by
encapsulation layer 26b (FIG. 8A) and encapsulation layer 26c (FIG. 8B).
The state of fluid 24 may be established at a pressure that is sufficient
to cause a gas to penetrate encapsulation layer 26b (FIG. 8A) and
encapsulation layer 26c (FIG. 8B) and diffuse through that layer and into
chamber 24.

[0085]Thus, in this set of embodiments, fluid 24 diffuses into chamber 22
through encapsulation layer 26a and/or encapsulation layer 26b. That
diffusion may cause or result in a "final" ambient pressure of fluid 24
(i.e., the pressure of fluid 24 after completion of MEMS 10 and/or after
deposition, formation and/or growth of encapsulation layer 26c (FIG. 8A)
and encapsulation layer 26d (FIG. 8B)) being within a selected,
predetermined and/or desired range of pressures.

[0086]In another set of embodiments, the ambient pressure of fluid 24
immediately after being "trapped" or "sealed" in chamber 24 may be
selected or designed to be less than the selected, predetermined and/or
desired range of mechanical damping of micromachined mechanical structure
12 required or desired during normal operation. After processing
encapsulation layer 26c (FIG. 8A) and encapsulation layer 26d (FIG. 8B),
the "final" ambient pressure of fluid 24 may be within the selected,
predetermined and/or desired range of pressures. In this way, the
subsequent micromachining processing causes a reduction in pressure of
fluid 24 such that the "final" pressure of fluid 24 provides the
selected, designed or predetermined mechanical damping of micromachined
mechanical structure 12.

[0087]It should be noted that, in these embodiments, it may be
advantageous to employ a metal bearing material (for example, silicides)
to form encapsulation layer 26c (FIG. 8A) and encapsulation layer 26d
(FIG. 8B). The encapsulation layer 26c (FIG. 8A) and encapsulation layer
26d (FIG. 8B) may be, for example deposited, formed or grown using, for
example, an epitaxial, a sputtering or a CVD-based reactor (for example,
APCVD).

[0088]In another aspect of the present invention, the MEMS may include a
plurality of monolithically integrated micromachined mechanical
structures having one or more electromechanical systems (for example,
gyroscopes, resonators, temperature sensors and/or accelerometers). The
micromachined mechanical structures may include mechanical structures
that are disposed in a corresponding chamber, which includes an
environment (i.e., fluid) providing a desired, predetermined, appropriate
and/or selected mechanical damping for the mechanical structures.

[0089]With reference to FIG. 9, in one embodiment, MEMS 10 includes a
plurality of micromachined mechanical structures 12a-c that are
monolithically integrated on or disposed within substrate 14. Each
micromachined mechanical structure 12a-c includes one or more mechanical
structures 20a-p (for the sake of clarity only a portion of which are
numbered).

[0091]In certain embodiments, fluids 24a-d are "trapped" and "sealed" in
chambers 22a-d, as described above, and maintained and/or contained at
the same or substantially the same selected, desired and/or predetermined
state. As such, in these embodiments, fluids 24a-d may provide the same
or substantially the same desired, predetermined, appropriate and/or
selected mechanical damping for mechanical structures 20a-p.

[0092]In other embodiments, fluids 24a-d are "trapped," "sealed,"
maintained and/or contained in chambers 22a-d, as described above, to
provide differing or different mechanical damping characteristics for
mechanical structures 20a-p. In this way, structure 12a may include, for
example, a resonator (requiring a Q of, for example, 10,000) and
structure 12d may include, for example, an accelerometer (requiring a Q
of, for example, 0.6). Accordingly, fluids 24a-d may provide
substantially different desired, predetermined, appropriate and/or
selected mechanical damping for mechanical structures 20a-p.

[0093]Indeed, in at least one embodiment, structure 12c includes a
plurality of chambers, namely chambers 22c and 22d, each containing fluid
24c and 24d, respectively. The fluids 24c and 24d may be "trapped,"
"sealed," maintained and/or contained in chambers 22c and 22d,
respectively, at the same or substantially the same selected, desired
and/or predetermined states. As such, in this embodiment, fluids 24c and
24d may provide the same or substantially the same desired,
predetermined, appropriate and/or selected mechanical damping for
mechanical structures 20h-k and 20l-p, respectively.

[0094]Alternatively, in at least another embodiment, fluids 24c and 24d
may be "trapped," "sealed," maintained and/or contained in chambers 22c
and 22d, respectively, at different or substantially different selected,
desired and/or predetermined states. In this embodiment, chambers 22c and
22d may be "sealed" using different processing techniques, different
processing conditions and/or different materials (for example, gases or
gas vapors). As such, after encapsulation, fluids 24c and 24d provide
different or substantially different mechanical damping characteristics
for mechanical structures 20h-k and 20l-p, respectively. In this way,
micromachined mechanical structure 12c may include different
electromechanical systems (for example, gyroscopes, resonators,
temperature sensors and accelerometers) that require different or
substantially different mechanical damping characteristics for optimum,
predetermined, desired operation.

[0095]It should be noted that in the embodiment illustrated in FIG. 9,
micromachined mechanical structures 12a-c may include the same features,
attributes, alternatives, materials and advantages, as well as be
fabricated in the same manner, as the mechanical structure 12 illustrated
in FIGS. 1-8C, and described above. For the sake of brevity, those
features, attributes, alternatives, materials, techniques and advantages
will not be restated here.

[0096]Moreover, the discussion above with respect to fluid 24 and/or fluid
24 in conjunction with FIGS. 3-8C is entirely, fully and completely
applicable to these sets of embodiments. For the sake of brevity, it will
not be repeated.

[0097]It should be further noted that the features, attributes,
alternatives, materials and advantages, as well as the fabrication
techniques, of the embodiment illustrated in FIG. 9 (and described above)
are fully and equally applicable to MEMS illustrated in FIGS. 1-8C. For
example, micromachined mechanical structure 12 of FIG. 3 may include a
plurality of chambers to maintain and/or contain fluids at the same,
substantially the same, different or substantially different selected,
desired and/or predetermined states (for example, micromachined
mechanical structure 12c of FIG. 9). Accordingly, the fluids in the
chambers may provide the same, substantially the same, different or
substantially different mechanical damping characteristics for mechanical
structures (for example, fluids 24c and 24d which are "trapped,"
"sealed," maintained and/or contained in chambers 22c and 22d of
micromachined mechanical structure 12c of FIG. 9). For the sake of
brevity, those features, attributes, alternatives, materials, techniques
and advantages will not be restated here. There are many inventions
described and illustrated herein. While certain embodiments, features,
materials, configurations, attributes and advantages of the inventions
have been described and illustrated, it should be understood that many
other, as well as different and/or similar embodiments, features,
materials, configurations, attributes, structures and advantages of the
present inventions that are apparent from the description, illustration
and claims. As such, the embodiments, features, materials,
configurations, attributes, structures and advantages of the inventions
described and illustrated herein are not exhaustive and it should be
understood that such other, similar, as well as different, embodiments,
features, materials, configurations, attributes, structures and
advantages of the present inventions are within the scope of the present
invention.

[0098]For example, it may be advantageous to employ gas species that are
compatible with the standard type reactors. In this way, any
modifications or customizations of the reactors to, for example, form,
grow or deposit second encapsulation layer 26b, may be minimized and/or
eliminated.

[0099]Further, it may be advantageous to employ gas species that are
relatively inexpensive and available to the reactor/fabrication facility.
In this way, the costs of MEMS 10 may be minimized and/or reduced.

[0100]The term "depositing" means, among other things, depositing,
creating, forming and/or growing a layer of material using, for example,
a reactor (for example, an epitaxial, a sputtering or a CVD-based reactor
(for example, APCVD, LPCVD, or PECVD)).

[0101]Finally, it should be further noted that while the present
inventions have been described in the context of microelectromechanical
systems including micromechanical structures or elements, the present
inventions are not limited in this regard. Rather, the inventions
described herein are applicable to other electromechanical systems
including, for example, nanoelectromechanical systems. Thus, the present
inventions are pertinent to electromechanical systems, for example,
gyroscopes, resonators, temperatures sensors and/or accelerometers, made
in accordance with fabrication techniques, such as lithographic and other
precision fabrication techniques, which reduce mechanical components to a
scale that is generally comparable to microelectronics.